Flexible wet friction materials including silanes

ABSTRACT

A method for forming a friction material. The method includes mixing a fibrous base material and filler particles to form a substrate. The method further includes saturating the substrate with a silane solution including a silane to form a uniformly impregnated silane matrix. The method also includes curing the uniformly impregnated silane matrix to form a cured uniformly impregnated silane matrix. The method also includes saturating the cured uniformly impregnated silane matrix with a phenolic resin solution to form a uniformly impregnated silane, phenolic resin matrix. The method also includes curing the uniformly impregnated silane, phenolic resin matrix to form the friction material.

TECHNICAL FIELD

The present disclosure relates to a wet friction material for clutchpads, in particular, a flexible wet friction material having higherperformance characteristics, e.g., flexibility.

BACKGROUND

Known friction materials for clutches include a fibrous base materialand a filler material. The fibrous base material forms a structure forthe friction material and the filler material is configured to createfriction. Known friction materials further include a binder, such as aphenolic resin. Phenolic resins are known to have a high crosslinkdensity that could cause friction materials to become brittle. It isdesired to enhance the flexibility of friction materials to reduce thepossibility of glazing and hot spot formation.

SUMMARY

According to one embodiment, a method for forming a friction material isdisclosed. The method includes mixing a fibrous base material and fillerparticles to form a substrate. The method further includes saturatingthe substrate with a silane solution including a silane to form auniformly impregnated silane matrix. The method also includes curing theuniformly impregnated silane matrix to form a cured uniformlyimpregnated silane matrix. The method also includes saturating the cureduniformly impregnated silane matrix with a phenolic resin solution toform a uniformly impregnated silane, phenolic resin matrix. The methodalso includes curing the uniformly impregnated silane, phenolic resinmatrix to form the friction material. The fibrous base material may havea porosity of 45 to 80%. In another variation, the fibrous base materialmay have a porosity of 50 to 65%. The first curing step may includecuring the uniformly impregnated silane matrix at ambient temperaturefor 20 to 28 hours. The first curing step may include curing stepincludes curing the uniformly impregnated silane matrix at an elevatedtemperature for 8 to 12 minutes. The elevated temperature may be in arange of 80 to 120° C. The filler particles may be silica containingparticles, which may be diatomaceous earth particles.

According to another embodiment, a method for forming a frictionmaterial is disclosed. The method includes mixing a fibrous basematerial and filler particles to form a substrate, saturating thesubstrate with a silane solution including a silane to form a uniformlyimpregnated silane matrix, curing the uniformly impregnated silanematrix to form a cured uniformly impregnated silane matrix, saturatingthe cured uniformly impregnated silane matrix with a non-silane bindersolution to form a uniformly impregnated silane, non-silane matrix, andcuring the uniformly impregnated silane, non-silane matrix to form thefriction material. The silane may include an amino functional group anda silanol functional group. The silane solution may include an organicsolvent. The fibrous base material may have a porosity of 45 to 80%. Inanother variation, the fibrous base material may have a porosity of 50to 65%. The filler particles may be silica containing particles, whichmay be diatomaceous earth particles.

In another embodiment, a friction material for a clutch is disclosed.The friction material includes a fibrous base material, fillerparticles, a silane binder comprising 3 to 10 weight % based on a totalweight of the friction material, and a non-silane binder comprising 25to 32 weight % based on the total weight of the friction material. Thesilane binder may include an amino functional group and a silanolfunctional group. The non-silane binder may be a phenolic resin binder.The silane binder may include an organosilane binder. The fibrous basematerial and the filler particles may comprise 65 to 72 weight % basedon the total weight of the friction material.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature and mode of operation of aspects will now be more fullydescribed in the following detailed description taken with theaccompanying drawing figures, in which:

FIG. 1 illustrates a schematic cross-section view of a friction materialused on a clutch plate according to an example aspect;

FIG. 2 illustrates a cross-sectional view of a torque converter having afriction material according to an example aspect; and

FIG. 3 illustrates a flowchart for a process of producing a frictionmaterial according to an example aspect.

DETAILED DESCRIPTION

At the outset, it should be appreciated that like drawing numbersappearing in different drawing views identify identical, or functionallysimilar, structural elements. Furthermore, it is understood that thisdisclosure is not limited only to the particular embodiments,methodology, materials and modifications described herein, and as suchmay, of course, vary. As those of ordinary skill in the art willunderstand, various features illustrated and described with reference toany one of the figures can be combined with features illustrated in oneor more other figures to produce embodiments that are not explicitlyillustrated or described.

The terminology used herein is for the purpose of describing particularaspects only, and is not intended to limit the scope of the presentdisclosure, which is limited only by the appended claims. It is to beunderstood that the disclosed embodiments are merely examples and otherembodiments can take various and alternative forms. The figures are notnecessarily to scale; some features could be exaggerated or minimized toshow details of particular components. Therefore, specific structuraland functional details disclosed herein are not to be interpreted aslimiting, but merely as a representative basis for teaching one skilledin the art to variously employ the embodiments.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. Although any methods, devicesor materials similar or equivalent to those described herein can be usedin the practice or testing of the disclosure, the following examplemethods, devices, and materials are now described.

The term “substantially” may be used herein to describe disclosed orclaimed embodiments. The term “substantially” may modify a value orrelative characteristic disclosed or claimed in the present disclosure.In such instances, “substantially” may signify that the value orrelative characteristic it modifies is within ±0%, 0.01%, 0.05%, 0.1%,0.2%, 0.3%, 0.4%, or 0.5% of the value or relative characteristic.

Flexibility of wet friction materials is important to reduce thepossibility of glazing and hot spot formation. Phenolic resin is acommonly used binder material for wet friction materials. Certainphenolic resins have a high crosslink density that may make the wetfriction material become brittle. Known proposals use silane as anadditional binder material to improve the flexibility of the frictionmaterial.

In certain applications, suitable pH conditions for silane curing is apH less than 7. If the silane is cured under basic conditions (i.e.,pH>7), the silane may rapidly gelate and crosslink with itself, therebybecoming less effective as a flexibility agent. Mixing a silane solutionand a phenolic resin solution to form a binder material may cause the pHof the solution mixture to reach a pH of 8 or above. It is desired toprovide a wet friction material production method that accommodatessuitable pH conditions for silane curing. In one or more aspects,production methods and related wet friction materials are disclosed thatimprove the functionality of silane within wet friction materials (e.g.,increasing the flexibility of wet friction materials).

With reference to FIG. 1, a cross-sectional view of friction material 10is shown. Friction material 10 is used on clutch plate 12. Frictionmaterial 10 may be fixedly secured to plate 12. Friction material 10includes fibrous base material 14. Fibrous base material 14 may be anorganic or inorganic fiber, for example but without limitation,cellulose fibers, cotton fibers, aramid fibers, carbon fibers, orcombinations thereof.

Friction material 10 also includes filler material 16. A filler material(e.g., filler particles) may be arranged for carrying a frictionmodifier and may be characterized as: (a) capable of having surfaceinteractions with a friction modifier; (b) having a particle shapeconfigured to carry a friction modifier; (c) having a particle sizeconfigured to carry a friction modifier; (d) having pores for carrying afriction modifier; or (e) any combination of (a) through (d). In anexample aspect, the filler material may include silica. In an exampleaspect, the silica containing particles are useful to carry, to beavailable to, to attract, or to encapsulate a friction modifier.

A friction modifier may refer to an additive, component, or ingredientin automatic transmission fluid (ATF) as used in automotive components,such as wet clutches or torque converters. In one example aspect, thefriction modifier is configured to provide compatibility between platesof a metal clutch and compatibility between the ATF and the wet clutchor the torque converter. Friction modifiers interact with metal surfaceswith polar heads of the friction modifier bonding to the clutch metalsurfaces and repulsive forces from the tails of the molecules, forexample, aiding in separation of the metal surfaces.

Typical friction modifiers include fatty amines, fatty acids, fattyamides, fatty esters, paraffin waxes, oxidized waxes, fatty phosphates,sulfurized fats, long chain alkylamines, long chain alkylphosphites,long chain alkylphosphates, and borated long chain polars. In an exampleaspect, the friction modifier comprises a generally straight oleophilictail portion including 10 to 24 carbons as well as an active polar headgroup portion. In another example aspect, the tail portion includes 18to 24 carbons. The head portions form layers on the friction surfaces bysurface absorption. Friction modifiers are configured to not corrode orcause degradation to the filler material or the clutch plate, which istypically made of steel. A non-limiting example of a friction modifieruseful in an example aspect is octadecylamine.

In an example aspect, the filler material is comprised of silicacontaining particles. The silica containing particles may carry, beavailable to, attract or encapsulate a friction modifier. In one exampleaspect, the silica containing particles may be diatomaceous earth (DE)particles. DE is a natural silica source formed from sedimentation ofsingle cell aquatic organisms called diatoms. DE can form in marine orfresh water environments and exhibit properties that are related totheir unique shape and structure. These properties will vary accordingto the diatom species found in each deposit, each with differingchemistries, shape factors, and pore structures. Some non-limitingexamples of silica containing carrier particles include Celite® 281,DiaFil® 230, and CelTiX™. Celite® 281 is a flux-calcinated diatomaceousearth of plankton marine diatomite. DiaFil® 230 is a naturaldiatomaceous earth material. CelTiX™ is a fine, natural freshwaterdiatomaceous earth product with excellent reinforcing ability in mosttypes of elastomers. Silica is also referred to as silicon dioxide orSiO₂. The diatomaceous earth generally contains about ten percent otheroxides besides silica and is substantially devoid of crystalline silica.Typically, diatomaceous earth is amorphous.

Friction material 10 also includes binder 18. Binder 18 may be phenolicresin. Phenolic resin upon curing forms water as a byproduct of areaction between a phenol and a formaldehyde. Arofene® 295-E-50 is anon-limiting example of a phenolic resin that can be used with frictionmaterials. Using phenolic resin as the binder may result in the frictionmaterial that is too stiff. A friction material that becomes too stiffmay lead to poor performance and durability issues. To increase theflexibility of wet friction materials, phenolic resin is at leastpartially replaced by silane as a binder component in the wet frictionmaterial.

FIG. 2 illustrates a cross-sectional view of torque converter 100 havingfriction material 10 according to an example aspect. Torque converter100 includes cover 102, impeller 104 connected to cover 102, turbine 106in fluid communication with impeller 104, stator 108, output hub 110arranged to non-rotatably connect to an input shaft (not shown) for atransmission, torque converter clutch 112 and vibration damper 114.Clutch 112 includes friction material 10 and piston 116. Piston 116 isdisplaceable to engage friction material 10 with piston 116 and cover102 to transmit torque from cover 102 to output hub 110 through frictionmaterial 10 and piston 116. Fluid 118 is used to operate clutch 112.Friction material 10 may be used in any clutch device for any torqueconverter configuration.

FIG. 3 depicts a flowchart of process 200 that may be utilized toproduce friction material 10. As shown in FIG. 3, process 200 includesmultiple steps 202, 204, 206, 208 and 210. In certain aspects, one ormore of these steps may be modified or omitted depending on theimplementation.

In step 202 of process 200, a substrate is formed. The substrate may beformed by mixing a fibrous base material and filler particles. Theporosity (e.g., void volume) of the fibrous base material may be any ofthe following values or within a range of any two of the followingvalues: 45, 50, 55, 60, 65, 70, 75 and 80%. The fibrous base materialmay be an organic or inorganic fiber, for example but withoutlimitation, cellulose fibers, cotton fibers, aramid fibers, carbonfibers, or combinations thereof. The filler material may be silicacontaining particles, e.g., DE particles.

In step 204 of process 200, the substrate is saturated with a silanesolution including a silane to from a uniformly impregnated silanematrix. As used in one or more embodiments herein, uniformly impregnatedrefers to the substrate (or other impregnated material as disclosedherein) receiving a uniform amount (by volume or weight) of the silanesolution (or other impregnating solution as disclosed herein) throughoutthe volume of the substrate (or other impregnated material). The uniformimpregnation results in no substantial volume of the substrate (or otherimpregnated material) having a substantially higher or lower amount ofthe silane solution (or other impregnating solution) than the bulkvolume of the substrate (or other impregnated material). In one or moreembodiments, the uniform impregnation does not form a localized region,e.g., a surface coating of the silane solution (or other impregnatingsolution) or a silane (or other solid material in the impregnatingsolution) once cured. Rather, in these embodiments, the impregnatingsolution or solid material in the impregnating solution is substantiallyevenly distributed through the volume of the impregnated material.

In one aspect, the substrate does not include any other binder material,e.g., a phenolic resin, when step 204 is carried out. In one aspect, thesilane solution only includes silanes and no non-silane binders, e.g., aphenolic resin. The absence of phenolic resin or other binders permitsthe pH of the silane solution to be less than 7. The acidic pH of thesilane solution reduces crosslinking of the silane, thereby beneficiallyincreasing the formation of bonds between the organic and inorganicmaterials within the friction material. Accordingly, reducing thecrosslinking of the silane is a benefit of one or more aspects.

A silane is a monomeric silicon compound with four substituent groupsattached to a silicon atom. These substituent groups can be nearly anycombination of nonreactive, inorganically reactive, or organicallyreactive groups. Inorganic reactivity represents the covalent bondsformed through oxygen to the silicon atom to form a siloxane type ofbond. Organic reactivity occurs on the organic portion of the moleculeand does not directly involve the silicon atom. Silanes are useful innumerous applications as adhesion promoters, crosslinking agents, waterscavengers, and/or coupling agents.

The silane solution may include an organic solvent (e.g., ethanol,methanol, methoxypropanol, ethylene glycol, toluene and tetrahydrofuran)and one or more silane compounds. Non-limited examples of silanesolutions that may be utilized include Dynasylan® HYDROSIL 2627, 2776,2909, 2926, 1151, 1153, 2907 and 2775, Dynasylan® F 8815, Dynasylan® VPSHYDROSIL 2990 and 2975, and Dynasylan® SIVO 110, 111, 112, 113, 121,160, 140, 608 and 850, available from Evonik Corp. of Essen, Germany. Inanother embodiment, the silane solution may include an organic solventand an aqueous solution including silane. The silane may have astability of at least three (3) months in an aqueous solution having apH of 3 to 5. The silane may be one or more of the following functionalgroups: amino, alkyl, silanol, diamino, diol, vinyl, triamino,fluoroalkyl, acrylic, acrylamide, quaternary ammonium and siliconate.

In step 206 of process 200, the uniformly impregnated silane matrix,which includes the silane solution, is cured. During the curing step,the pH of the silane solution may be any of the following values orwithin a range of any two of the following values: 3, 4, 5, 6 and 7. Theconditions of the curing step may vary according to amount of silanesolution and environmental conditions, for example. In one aspect, theuniformly impregnated silane matrix may be cured at ambient temperaturesfor a pre-determined amount of time. The predetermined amount of timemay be any of the following values or within a range of any two of thefollowing values: 20, 22, 24, 26 and 28 hours. In another aspect, theuniformly impregnated silane matrix may be cured at a predeterminedelevated temperature for a predetermined amount of time. Thepredetermined elevated temperature may be any of the following values orwithin a range of any two of the following values: 80, 90, 100, 110 and120° C. The predetermined amount of time may be any of the followingvalues or within a range of any two of the following values: 8, 9, 10,11 and 12 minutes. By curing the silane prior to the addition of thephenolic resin solution, the silane's functionality as a coupling agentwith silica containing filler particles is enhanced. This enhancementprovides good characteristics to the resulting wet friction material. Inone embodiment, a glazing test is performed on the resulting frictionmaterial. The glazing test may be conducted on a S.A.E. No. 2 stand.According to the test, the friction material is slipped for a relativelong period of time with a limited amount of ATF. The friction materialfails by glazing when the surface temperature increased past a thresholdtemperature. By curing the silane prior to the addition of the phenolicresin solution, the lifetime of the friction material according to thisglazing step may be increased by any of the following values or within arange of any two of the following values: 10, 20, 30, 40 and 50%.

In step 208 of process 200, the cured uniformly impregnated silanematrix is saturated with a phenolic resin solution. Non-limitingexamples of solvents in the phenolic resin solution include ethanol,methanol and n-butanol. Arofene® 295-E-50 is a non-limiting example of aphenolic resin that can be used with friction materials. The weight % ofphenolic resin in the phenolic resin solution may be any of thefollowing values or within a range of any two of the following values:47, 48, 49, 50, 51, 52 and 53 weight %.

In step 210 of process 200, the uniformly impregnated silane, phenolicresin matrix, which includes the phenolic solution, is cured. Theconditions of the curing step may vary according to amount of phenolicresin solution and environmental conditions, for example. In one aspect,the uniformly impregnated silane, phenolic resin matrix may be cured atambient temperatures for a pre-determined amount of time. Thepredetermined amount of time may be any of the following values orwithin a range of any two of the following values: 5, 10, 15, 20, 25 and30 minutes. In another aspect, the uniformly impregnated silane,phenolic resin matrix may be cured at a predetermined elevatedtemperature for a predetermined amount of time. The predeterminedelevated temperature may be any of the following values or within arange of any two of the following values: 150, 160, 170, 180, 190 and200° C. The predetermined amount of time may be any of the followingvalues or within a range of any two of the following values: 5, 10, 15,20, 25 and 30 minutes.

The process of FIG. 3 may be used to produce a friction material for aclutch. In one aspect, the friction material includes a fibrous basematerial, filler particles, a silane binder and a non-silane binder. Theweight % of silane binder in the friction material may be any of thefollowing values or within a range of any two of the following values:3, 4, 5, 6, 7, 8, 9 and 10 weight %. The weight % of non-silane binder(e.g., phenolic resin) in the friction material may be any of thefollowing values or within a range of any two of the following values:25, 26, 27, 28, 29, 30, 31 or 32 weight %. The weight % of the fibrousbase material and the filler particles, cumulatively, may be any of thefollowing values or within a range of any two of the following values:65, 66, 67, 68, 69, 70, 71 and 72 weight %. The porosity (e.g., voidvolume) of the fibrous base material may be any of the following valuesor within a range of any two of the following values: 45, 50, 55, 60,65, 70, 75 and 80%.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, to the extentany embodiments are described as less desirable than other embodimentsor prior art implementations with respect to one or morecharacteristics, these embodiments are not outside the scope of thedisclosure and can be desirable for particular applications.

PARTS LIST

The following is a list of reference numbers shown in the Figures.However, it should be understood that the use of these terms is forillustrative purposes only with respect to one embodiment. And, use ofreference numbers correlating a certain term that is both illustrated inthe Figures and present in the claims is not intended to limit theclaims to only cover the illustrated embodiment.

Friction Material 10

Clutch Plate 12

Fibrous Base Material 14

Filler Material 16

Binder 18

Torque Converter 100

Cover 102

Impeller 104

Turbine 106

Stator 108

Output Hub 110

Clutch 112

Vibration Damper 114

Piston 116

Fluid 118

Process 200

Step 202

Step 204

Step 206

Step 208

Step 210

What is claimed is:
 1. A method for forming a friction materialcomprising: mixing a fibrous base material and filler particles to forma substrate; saturating the substrate with a silane solution including asilane to form a uniformly impregnated silane matrix; curing theuniformly impregnated silane matrix to form a cured uniformlyimpregnated silane matrix; saturating the cured uniformly impregnatedsilane matrix with a phenolic resin solution to form a uniformlyimpregnated silane, phenolic resin matrix; and curing the uniformlyimpregnated silane, phenolic resin matrix to form the friction material.2. The method of claim 1, wherein the fibrous base material has aporosity of 45 to 80%.
 3. The method of claim 2, wherein the fibrousbase material has a porosity of 50 to 65%.
 4. The method of claim 1,wherein the first curing step includes curing the uniformly impregnatedsilane matrix at ambient temperature for 20 to 28 hours.
 5. The methodof claim 1, wherein the first curing step includes curing step includescuring the uniformly impregnated silane matrix at an elevatedtemperature for 8 to 12 minutes.
 6. The method of claim 5, wherein theelevated temperature is in a range of 80 to 120° C.
 7. The method ofclaim 1, wherein the filler particles are silica containing particles.8. The method of claim 7, wherein the silica containing particles arediatomaceous earth particles.
 9. A method for forming a frictionmaterial comprising: mixing a fibrous base material and filler particlesto form a substrate; saturating the substrate with a silane solutionincluding a silane to form a uniformly impregnated silane matrix; curingthe uniformly impregnated silane matrix to form a cured uniformlyimpregnated silane matrix; saturating the cured uniformly impregnatedsilane matrix with a non-silane binder solution to form a uniformlyimpregnated silane, non-silane matrix; and curing the uniformlyimpregnated silane, non-silane matrix to form the friction material. 10.The method of claim 9, wherein the silane includes an amino functionalgroup and a silanol functional group.
 11. The method of claim 9, whereinthe silane solution includes an organic solvent.
 12. The method of claim9, wherein the fibrous base material has a porosity of 45 to 80%. 13.The method of claim 12, wherein the fibrous base material has a porosityof 50 to 65%.
 14. The method of claim 9, wherein the filler particlesare silica containing particles.
 15. The method of claim 14, wherein thesilica containing particles are diatomaceous earth particles.
 16. Afriction material for a clutch comprising: a fibrous base material;filler particles; a silane binder comprising 3 to 10 weight % based on atotal weight of the friction material; and a non-silane bindercomprising 25 to 32 weight % based on the total weight of the frictionmaterial.
 17. The friction material of claim 16, wherein the silanebinder includes an amino functional group and a silanol functionalgroup.
 18. The friction material of claim 16, wherein the non-silanebinder is a phenolic resin binder.
 19. The friction material of claim16, wherein the silane binder includes an organosilane binder.
 20. Thefriction material of claim 16, wherein the fibrous base material and thefiller particles comprise 65 to 72 weight % based on the total weight ofthe friction material.